The present invention relates to a semiconductor laser and, more particularly, to a semiconductor laser which operates at room temperature in a fundamental transverse-oscillation mode to emit visible light.
As is generally known, semiconductor lasers have a multilayer structure, each including a semiconductive substrate, cladding layers of GaAlAs, an active layer of GaAs, a current-blocking layer of GaAs, and the like. One of the cladding layers is formed above the active layer. A channel groove is cut in the upper surface of this cladding layer for blocking a current and guiding the light generated in the laser. To manufacture such a multilayer laser, it is required that the recrystallization of each layer be strictly controlled to impart uniform and good crystallinity to the layer. Unless this requirement is fulfilled, the laser will have but a low oscillation stability and, hence, will fail to operate reliably.
Recently, a vapor-phase growing method called "metal organic chemical vapor deposition (MOCVD)" has been developed to take the place of the liquid-phase epitaxy (LPE) method which has been used for some time. The MOCVD method can substantially satisfy the the condition required in recrystallizing the layers of the semiconductor laser. It is, therefore, preferred as a method which can produce a greatly reliable semiconductor laser. This method, however, is disadvantageous in that crystals having a high light-emitting efficiency must be grown on that surface of a layer in which a channel groove is cut. Highly reliable GaAlAs lasers having channel grooves have yet to be reported.
Semiconductor materials for lasers, such as InGaAsP, InGaAlAs and InGaAlP, are now attracting attention. This is because semiconductor lasers made of these materials emit laser beams with such a broad wavelength range that they can be used in optical communication systems or in optical data storage systems. These semiconductor materials can indeed be formed by the vapor-phase growth method. However, no reports have been made of a semiconductor laser which is made of InGaAlAs and InGaAlP or the line, and which can continuously emit stable visible light at room temperature in a fundamental transverse-oscillation mode. The reason is because these materials must be formed under strictly controlled conditions in order to have a crystal lattice well aligned with that of the substrate. In practice, it is extremely difficult to successfully control these conditions. Were a semiconductor laser made of any one of these materials, it would have its basic characteristic degraded quickly (for example, within about one hour), and would thus become useless.